With each request, ACT-sysmodule specifies request-header "X-Nintendo-Device-Model". This is the only *dedicated* request-header that's contains anything Old3DS/New3DS specific. This was implemented with 9.0.0-X, and presumably 8.1.0-0_New3DS. The value is from a string initialized during ACT-sysmodule startup. The value-string is the codename string for all 5 of the model values from Cfg:GetSystemModel. When the output from GetSystemModel is >=5(switch statement default case), it runs this: "len = snprintf(outstr, outmaxsize, "3DS-%u", model);"